Periodic trends/ Acid Bases

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jmali921
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37326
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Periodic trends/ Acid Bases
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2010-09-27 19:36:54
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Organic Chemistry
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Acids/Base reaction
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  1. Brontsted-Lowry Acid is...
    proton donor (BAD -bronsted acid donor)
  2. Bronsted-Lowry Base is...
    proton acceptor (BBD-Bronsted base donor)
  3. A Lewis Acid is a...
    • electron pair acceptor (LAEA)
    • can be an electron pair defiecient species that can accept an electron pair
    • doesnt need H+ to be an acid
  4. A Lewis Base is a...
    • Electron pair donor (LBED)
    • all Bronsted Bases are Lewis Bases
  5. define: Inductive Effect
    the effect of a nearby dipole in a molecule on a reaction elsewherein that molecule.
  6. Name 5 characteristics that effect the acidity of a H on an molecule?
    • the molecule the H is bonded to (periodic trends)
    • Inductive Effects (e- withdrawing groups/ electronegativity)
    • Hydrogen Bonding (only in Fluorine,Oxygen, and Nitrogen FON)
    • Hybridization (more S-character = more acidic as the e- is held closer to nucleus)
    • Resonance(more resonance = more stable)
  7. For the following compound which of the carbons are involved in the delocalized pi system?

    C1H3-C2H=C3H-C4H=C5H2
    2-3-4-5
  8. Which of the following is the conjugate acid of water?

    a)OH-
    b)H20
    c)H30+
    d)H703+
    c) H30+
  9. Which of the following have an effect on the rate of an acid/base reaction?

    a. strength of the acid
    b. orientation of the collision
    c. activation energy
    d. concentration
    b and c.
  10. define: stereoelectric requirement. Explain in terms of an acid-base reaction.
    The 3D molecular orientation required in a reaction for a reaction to occur. In the case of an acid-base reaction, the H must be oriented with the unshared pair of electrons upon collision
  11. True/false: the more electronegative the atom bonded to the hydrogen, the more acid the hydrogen?
    True. Because of the increasing stability of the conjugate base as the electronegativity of an atom increases, acidity increases from left to right in a row of the periodic table.
  12. The higher the period of the atom bonded to hydrogen the lower the acidity of the molecule.
    True. When comparing a column, electronegativity is no longer the controlling factor. Acidity increases from top to bottom in a column of the periodic table, whereas electronegativity increases. Atoms lower in the column form weaker H bonds because their large atomic orbitals do not overlap as well with the small hydrogen 1s orbital. Weaker bonds make removing the proton easier. The ability of larger anions to better accomodate a negative charge also contributes to this trend.
  13. True/false: Inductive effect is the effect of a nearby dipole on the acidic proton in a molecule.
    True. Inductive effect deals with electron withdrawing groups that pull electrons away from the hydrogen making deprotanation easier.
  14. Hydrogen bonding within the molecule ______________ the acidity of a molecule
    Decreases. It is more difficult for a base to remove the hyrogen if the hydrogen bond must be broken in addition to the original sigma bond . However, this effect is complicated by the inductive effect of the group involved in the hydrogen bond.
  15. True/false: Ethyne is more acidic than ethane because of its hybridization?
    • True. Consider stability of unshared electrons in the conjuate bases of each compound. The unshared electron pair of ethan occupies sp3, while ethyne has an unshared pair of electrons in a sp orbital which is lower energy. Lower energy = greater stability.
    • .
  16. Resonance stabilization of the conjugate base increases the acidity of the molecule.
    True. The more resonance structures a molecule has, the lower energy it will have. Delocalization.
  17. Nucleophiles are usually acids.
    False. A nucleophile is an electron-rich species that seeks an electron-poor site; similar to a Lewis base.
  18. A molecule can be both an electrophile and a nucleophile.
    False. Think how can a species be both electron-rich and electron-poor?
  19. CH3COOH is _____________ acidic than sulfuric acid.
    weaker. H2S04 is obviously more acidic.
  20. A hydrogen attached to a double bonded carbon is less acidic than a hydrogen attached to a singly bonded carbon.
    False. Hybridization of the conjuagate base is provides stablility in a double-bonded carbon more than compared to the single bonded carbon.
  21. Which of the following is not an intermolecular force?

    A)Ion - dipole interactions
    B)London Dispersion forces
    C)Ion - ion interactions
    D)Dipole - dipole interactions
    C) Ion-ion interactions
    (this multiple choice question has been scrambled)
  22. A DU of two suggests which of the following structural features?

    A)a ring and a triple bond
    B)a double bond
    C)a ring
    D)a triple bond
    D) a triple bond

    remember: Degree of Unsaturation = [2 + (2 x #Carbons) + #Nitrogens - #Hydrogens - #Halogens]/2

    DU = 2 than either;


    two double bonds
    or one double bond and one ring
    or two rings
    or one triple bond
    (this multiple choice question has been scrambled)
  23. What effect does nitrogen have on the DU?
    It increases maximum number of Hydrogens by 1.
  24. As bond length increases, bond strength _________.
    decreases.
  25. ________ points increase with increased branching (or sphericity)
    melting
  26. Small (low molecular mass) nonpolar compounds have low melting points
    • true.
    • Higher melting points: Ionic compounds > Polar compounds > Nonpolar compounds
  27. Which of the following is not an isomer of the other compounds?

    a)3-hexene
    b)2,3-dimethyl-2-butene
    c)cyclohexane
    d)hexane
    cyclohexane
  28. A radical always has a positive charge.
    False.

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